1. Field of the Invention
This invention relates to a recording method for magneto-optic memory medium, and more particularly, to a recording method for magneto-optic memory medium including an overwriting to the magneto-optic memory medium by the use of a magnetic field modulating process wherein the writing and verifying of data is simultaneously performed.
2. Description of the Related Art
A thin film of amorphous rare earth-transition metal alloy, such as GdCo, TbFe, GdNdFe, GdTbFe and the like (hereinafter abbreviated as RE-TM film) has been used as a memory medium in a magneto-optic disc device since it has suitable characteristics for magneto-optic recording. Particularly known is a magneto-optic memory medium having an exchange-coupled double-layered structure in which a rccording layer of a low Curie point and a high coercive force and a reading layer of a high Curie point and a low coercive force are laminated to improve a reading efficiency of written data ("Magnetization Process of Exchange-Coupled Ferrimagnetic Double-Layered Films", Japanese Journal of Applied Physics, Vol. 20, No. 11, November 1981 pp. 2089-2095).
Recording in the exchange-coupled magneto-optic memory medium is performed by applying an optical beam for heating and a magnetic field to the memory medium to write a predetermined data in the writing layer. After writing (and cooling), the data is automatically transcribed to the reading layer having a high Kerr effect due to exchange-coupling by magnetization, and stably retained. Hence, reading can be stably carried out by the use of a Kerr effect of the reading layer which provides an excellent reading efficiency.
Rewriting in the magneto-optic memory medium is carried out usually by the steps (1) erasing of old data, (2) writing of new data, and (3) verification (confirmation of written data). The art at the primitive stage turns the disc once for each of the above steps, so that the disc requires to turn three times every rewriting.
In this regard, the so-called overwriting technique indispensable for a high speed recording process of information has been positively studied. A magnetic field modulation process is regarded as a most readily available and effcctive means among various configurations of the overwriting technique.
The overwrite technique which allows data to be overwritten performs the aforesaid steps (1) and (2) simultaneously, thereby making higher a speed of recording process of information.
The verification step (3) after overwriting in the above exchange-coupled magneto-optic memory medium is to be carried out in such a manner that the memory medium is cooled enough to cause data in the recording layer to be fully transcribed to the reading layer, then, the data is rcad therefrom to be checked. Hence, one more turn of the disc is required for the verification step after the overwriting. From this, it is desired to make further higher the speed of recording process, while the verification step is indispensable for ensuring reliability of written data and cannot practically be omitted.